This invention relates generally to expansion valves in refrigeration and air conditioning systems and in particular to an improved expansion valve which incorporates a reverse flow check valve.
Expansion valves are used in refrigerator and air conditioning systems and heating systems as flow control devices which restrict the flow of liquid refrigerant as it passes from the condensor to the evaporator. Essentially, expansion devices control the flow of liquid refrigerants so that it arrives at the evaporator at a uniform rate consistent with the heat transfer capability of the evaporator coil.
Such expansion devices fall generally into two categories, namely fixed orifice devices and variable orifice valves. In addition, variable orifice valves themselves may be separated into two general classes namely automatic valves and thermostatic valves.
Thermostatic expansion valves are disclosed in U.S. Pat. No. 2,786,336 (H. T. Lange), U.S. Pat. No. 3,742,722 (Leimbach) and U.S. Pat. No. 3,738,573 (Eschbaugh). The first two of these three patents are commonly owned by the owner of the present invention. U.S. Pat. No. 2,786,336 is directed to providing an expansion valve which compensates for any increased pressure differential across the valve port, for any increased pressure unbalance of the valve port and for any increase of suction temperature caused by the valve throttles, upon an increase of valve inlet or head pressure. U.S. Pat. No. 3,742,722 is directed toward providing an expansion valve in which the valve member is pressure balanced by way of an orifice therethrough which communicates the inlet port with a chamber defined by the valve housing and valve member, the inlet pressure thus acting on equal areas of opposite sides of the valve member. Finally, U.S. Pat. No. 3,738,573 is directed to the provision of an expansion valve of pressure balance construction for controlling flow in both large and small units. Later improvements are disclosed in U.S. Pat. No. 4,852,364, also commonly owned, and provide a means of combining an expansion and check valve as one discrete valve.
In some refrigeration and air conditioning systems, and heat pumps represent a prime example, it is necessary to provide for reverse refrigerant flow in the system. If any of the known expansion valves, such as those disclosed in the three patents discussed above are used in the system, it is necessary to provide parallel piping for an independent check valve in addition to the expansion valve. In the normal flow direction, the check valve closes and the refrigerant flow is directed to the expansion valve. In the reverse flow direction, the check valve opens to allow refrigerant to bypass the expansion valve. Systems of this type are not only cumbersome but tend to be expensive. With respect to the improvement disclosed in U.S. Pat. No. 4,852,364, of which the present invention represents a further improvement, the combination expansion and check valve solves this problem to a large extent by providing a check valve element which is disposed in the direct flow line between the inlet and outlet. However, this combination valve does not always solve the problem and tends not to be cost effective in some situations.
The present invention solves these problems in a manner not disclosed in the known prior art.